Pre-formed insulated ductwork products for carrying gasses in, for example, air conditioning systems and are used throughout the building and construction industry particularly due to their relatively fast speed of erection and relatively low cost compared to metal or plastic pipe work that must be subsequently lagged. An example of such pre-formed insulated ductwork is shown in UK Patent Publication number GB1,137,121 to Lo-Dense Fixings (Rugby) Limited which discloses providing longitudinal channels in a plastics foam material with a backing material which can be folded into a square or a circular cross sectioned insulated ducting. Other examples are shown in U.S. Pat. No. 6,148,867 which also discloses providing longitudinal channels in a fibrous and/or cellular foam insulation material with a moisture facing outer material which can be folded into a circular cross sectioned insulated ducting. Other broadly similar systems are disclosed in International Patent Publication number WO8504922 and Dutch Patent Publication number NL7502320.
However, such conventional systems suffer from the disadvantage that they cannot be used for ducting liquid as the liquid can ruin the insulating material. Furthermore, the open nature of the insulation material to the airflow passing through the ducting can mean that bugs/diseases etc. are more likely to be able to survive and colonise in the shelter of the insulation joints, thus causing an increased health risk. Moreover, the open nature of the insulation material can also mean that dust from the insulation material could become airborne into the air passing along the throughbore, again causing an increased health risk.